Viral infections of the heart are among the most commonly identified causes of acute myocarditis in children and adults and have been implicated in dilated cardiomyopathy. Although there is considerable information regarding the cellular immune response in viral heart disease, little is known about innate signaling mechanisms within the infected cardiac myocyte that contribute to host defense against viral infection. Studies from this and other laboratories have identified the presence of a family of innate immune receptors in the heart termed Toll-like receptors (TLRs). Importantly, recent studies have shown that TLR3 and TLR4 mediated signaling contributes to the induction of anti-viral cytokines through the adaptor molecule termed Toll-interleukin-1 receptor (TIR) domain-containing adaptor inducing interferon-[unreadable] (TRIF). Our preliminary data in mice deficient in TLR3, TLR4 or TRIF show that the TLR3/4?TRIF signaling pathway is essential for the control of early viral replication, as well as the optimal induction of an anti-viral response in the heart. Based upon the foregoing observations the immediate specific objectives of this proposal will be to test the following hypotheses: (1) Signaling through TLR3 and TLR4 induces an anti-viral response in the hearts of enterovirus infected mice through a TRIF-dependent pathway, and (2) TRIF amplification of the antiviral response protects the heart against cytopathic injury, left ventricular dilatation and loss of myocardial contractility. Four Aims are envisioned. In Specific Aim 1 we will test the hypothesis that induction of the innate antiviral response in the heart following enteroviral infection is mediated by TLR3 and TLR4 via a TRIF-dependent pathway. Specific Aim 2 will test the hypothesis that loss of TLR3/TLR4?TRIF signaling will result in increased virus-induced cytopathic injury in the heart, leading to left ventricular dilatation and loss of myocardial contractility. Specific Aim 3 will test the hypothesis that overexpression of TRIF will protect cardiac myocytes from virus-induced cytopathic injury, augment the innate anti-viral response in the heart, and prevent the development of left ventricular dilatation and loss of myocardial contractility associated with an enteroviral infection. Specific Aim 4 will test the hypothesis that the TRIF mediated cardiac cytoprotection results from the ability of the N-terminal and C-terminal regions of TRIF to activate distinct antiviral mechanisms. Thus, the proposed studies should provide definitive new information regarding the mechanisms of activation, as well as the role of the innate immune system (TLRs) in viral heart disease. PUBLIC HEALTH RELEVANCE: Viral infection of the heart may cause severe heart failure and death in children and adults. There is no specific treatment for this disease and patients may eventually require heart transplantation. The studies proposed in this grant will give us a better understanding of the disease and may lead to improved treatment options.